One measure of performance of a resonant tank circuit (sometimes called a resonator), such as an inductive-capacitive (“LC”) oscillator circuit, is its “phase noise” performance. “Phase noise” is generally defined as rapid, arbitrary, transient fluctuations in the phase of the wave resonating in the resonant tank circuit.
With an LC oscillator circuit, phase noise predominantly comes from two sources. First, the effective resistance within the resonator will generate thermal noise. Second, since any real-world LC oscillator circuit is always lossy, an active circuit is needed to replenish the energy resonating within the resonator such that it maintains a constant amplitude of oscillation. This active circuit can contribute thermal noise, shot noise, recombination-generation noise, flicker noise and so on to the resonator.
Flicker noise is a particular problem when the oscillator is made in a complementary metal-oxide semiconductor (CMOS) process and the active circuit for replenishing that energy takes the form of metal-oxide semiconductor (MOS) transistors coupled in a feedback configuration. MOS transistors exhibit a higher flicker noise resulting from imperfections in the manufacturing process, in which electron traps are formed in the silicon to silicon-dioxide interface.
What is needed in the art is a method and a system to replenish stored energy into a resonant tank circuit that addresses at least some of the concerns of the prior art.